I see too many requests in google search with http://g.etfv.co/ (that is suggested before), and it seems take to long...

I test this one now (with it i don't see all these requests : it provide favicon silently):
//img.src = 'http://g.etfv.co/' + protocol + "://" + host; // As suggested by decembre
img.src = 'http://api.byi.pw/favicon?url=' + protocol + "://" + host; //OTHER service suggested by decembre

I found it here :
An alternative for http://g.etfv.co/{url} favicon services
http://stackoverflow.com/questions/22842262/an-alternative-for-http-g-etfv-co-url-favicon-services

What you think of it ?

Sorry for the slow reply, I was making a cup of tea.

For the moment we are using the service at www.google.com/s2 but I have noted down your services, and we could add them as fallbacks for the future.

The new version uses GM_xmlhttpRequest() on Ecosia and StartPage, to work around CSP.

If this works well enough, we could actually use that as the default (initial) way for all

Re: @joeytwiddle:

Sorry for the slow reply, I was making a cup of tea.

ROFL! :)